Chromatography Forum

I am running a sample. I ran it on two separate GCS twice so a total of four runs. I saw two contamination peaks at a consistent peak area on all four chromatograms. I then ran the sample on a third different GC. The peaks vanished! I presumed the peaks weren't carry over as the peak size was consistent. But I also felt peaks can't just disappear. Any ideas?

More information needed :
Is it manual or automatic injection ?
Did you inject from the same vial ?
What was the GC parameters?
Are all the gases supplied from the same line ?